When using a starter in cold climates, for example, a surface of a fixed contact provided on an electromagnetic switch might freeze.
To be specific, when a power supply terminal of the electromagnetic switch is cooled through a battery cable, a surface temperature of the fixed contact fixed to the power supply terminal is lowered so that water vapor in the air is condensed on a contacting surface and freezes.
When the electromagnetic switch is operated under this condition, since an ice layer is formed on the surface of the fixed contact that is the contacting surface of the movable contact, a problem of causing a conductive failure between the contacts may occur.
In contrast, as shown in FIG. 8A, forming a plurality of grooves 110 on a surface of a fixed contact 100 as a conventional technology is disclosed in the Japanese Utility Model Publication No. 54-88563.
According to this conventional technology, since a contacting area when the contact is abutting is reduced and a contact pressure per unit area is increased, it becomes possible to crush the ice layer formed on the surface of the fixed contact 100 by an impact force when the contact is abutting.
However, in the conventional technology mentioned above (Publication No. '563), since flat surfaces 120 are left between a number of grooves 110 formed on a surface of the fixed contact 100, that is, between the adjoining grooves 110, as shown in FIG. 8B, it is not possible to sufficiently increase the contacting pressure between the contacts.
For this reason, in the electromagnetic switch that is used in severe cold environmental conditions or has a structure difficult to discharge humidity, there is a possibility that ice-crushing force is insufficient.
In this case, the ON/OFF operation needs to be repeated for several tens of times in order to secure the conduction by crushing the ice on the contacting surface.
Further, even if the ice could be crushed, a process of eliminating the crushed ice from the contacting surface is required in order to secure the conduction between the contacts.
However, in the conventional technology, since a large number of grooves 110 are formed on the contacting surface, a surface area where the ice adheres increases compared with a flat contacting surface where no grooves 110 are formed, thus there is a possibility that the crushed ice is likely to remain within the grooves 110.
In other words, it is difficult to eliminate the crushed ice from the contacts.